On 10/27/14 14:44, Vitaly Kuznetsov wrote:
> Guard against issuing unsupported REQ_FUA and REQ_FLUSH was introduced
> in d11e61583 and was factored out into blkif_request_flush_valid() in
> 0f1ca65ee. However:
> 1) This check in incomplete. In case we negotiated to feature_flush =
> REQ_FLUSH
> and flush_op = BLKIF_OP_FLUSH_DISKCACHE (so FUA is unsupported) FUA request
> will still pass the check.
> 2) blkif_request_flush_valid() is misnamed. It is bool but returns true when
> the request is invalid.
> 3) When blkif_request_flush_valid() fails -EIO is being returned. It seems
> that
> -EOPNOTSUPP is more appropriate here.
> Fix all of the above issues.
>
> This patch is based on the original patch by Laszlo Ersek and a comment by
> Jeff Moyer.
>
> Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
> ---
> drivers/block/xen-blkfront.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 5ac312f..2e6c103 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -582,12 +582,14 @@ static inline void flush_requests(struct blkfront_info
> *info)
> notify_remote_via_irq(info->irq);
> }
>
> -static inline bool blkif_request_flush_valid(struct request *req,
> - struct blkfront_info *info)
> +static inline bool blkif_request_flush_invalid(struct request *req,
> + struct blkfront_info *info)
> {
> return ((req->cmd_type != REQ_TYPE_FS) ||
> - ((req->cmd_flags & (REQ_FLUSH | REQ_FUA)) &&
> - !info->flush_op));
> + ((req->cmd_flags & REQ_FLUSH) &&
> + !(info->feature_flush & REQ_FLUSH)) ||
> + ((req->cmd_flags & REQ_FUA) &&
> + !(info->feature_flush & REQ_FUA)));
> }
>
> /*
> @@ -612,8 +614,8 @@ static void do_blkif_request(struct request_queue *rq)
>
> blk_start_request(req);
>
> - if (blkif_request_flush_valid(req, info)) {
> - __blk_end_request_all(req, -EIO);
> + if (blkif_request_flush_invalid(req, info)) {
> + __blk_end_request_all(req, -EOPNOTSUPP);
> continue;
> }
>
>
Not sure if there has been some feedback yet (I can't see anything
threaded with this message in my inbox).
FWIW I consulted "Documentation/block/writeback_cache_control.txt" for
this review. Apparently, REQ_FLUSH forces out "previously completed
write requests", whereas REQ_FUA delays the IO completion signal for
*this* request until "the data has been committed to non-volatile
storage". So, indeed, support for REQ_FLUSH only does not guarantee that
REQ_FUA can be served.
Reviewed-by: Laszlo Ersek <ler...@redhat.com>
Thanks
Laszlo
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